In our previous report1 we discussed host-guest interactions in a series of Hofmann-type clathrates of the general formula: M(NH3)2M’(CN)4-2C6H6, where M is Ni, Fe, Co, Zn, Mn and Cd and M’ is Ni. It was found that the splitting of the band due to CH out-of-plane vibration in benzene, at liquid nitrogen temperature, (at around 985 cm-1), increases as the volume of the tetragonal unit cell decreases. A similar behaviour we recorded in a series of benzene clathrate compounds (isostructural with Hofmann-type clathrates) in which the M’ metal was replaced by Pt or Pd, and it was interpreted as a consequence of a »free« rotation in the benzene molecules at room temperature but hindered at low temperatures. The magnitude of the splitting of this band, at liquid nitrogen temperatures, for all the clathrates studied was correlated with the volume of the tetragonal unit cell and with the effective ionic radii of the octahedrally coordinated metal M and the square- planar coordinated metal M’. The slope of Ai< vs, V(Unitcell) is =-100 cm"1 nm-3
